TRILL Link Protocols Donald Eastlake Huawei Technologies July 20141Directory Assist

TRILL Switches Are Routers A TRILL switch forwarding a TRILL data packet logically discards the link header/trailer of the received packet, figures out which port(s) to forward it on, and adds the appropriate link header/trail on the sent packet, depending on the link technology. Forwarding a TRILL Data packet from a green technology link to a blue technology link and back. July 2014Directory Assist2 TRILL Switch Payload TRILL Switch Payload

TRILL Link Protocols A TRILL link protocol specification needs to: – Get a TRILL packet from one TRILL switch port to another TRILL switch port(s) on the link. – Specify one variation for interoperability. – Distinguish between TRILL Data packets and TRILL IS-IS packets. – If the link can have more than two ports on it, provide the address of the destination port(s). – Maybe other stuff depending on link technology. July 2014Directory Assist3

TRILL Link Protocols From the beginning (RFC 6325), the TRILL protocol specifications have been clear that, – while you have Ethernet over TRILL, – you do NOT always have TRILL over Ethernet. Note that use of the protocol on a link to transport TRILL packets between TRILL switches has almost no effect on scaling. Bandwidth, delay, loss rate, … are all more important than protocol. July 2014Directory Assist4

From RFC | Outer Ethernet Header | | TRILL Header | | Inner Ethernet Header | | Ethernet Payload | | Ethernet FCS | | PPP Header | | TRILL Header | | Inner Ethernet Header | | Ethernet Payload | | PPP FCS | July 2014Directory Assist5 TRILL over PPP: NO Ethernet Header before TRILL Header TRILL over Ethernet: Ethernet Header before TRILL Header

TRILL Link Protocols In TRILL over Ethernet, Ethertypes indicate TRILL Data (0x22F3) or TRILL IS-IS (0x22F4). [RFC 6325] In TRILL over PPP, PPP code points indicate TRILL Data (0x005D) or TRILL IS-IS (0x405D). [RFC 6361] July 2014Directory Assist | V | R |M|Op-Length| Hop Count | | Egress RBridge Nickname | Ingress RBridge Nickname | The 6-byte TRILL Data Header Ethertype 0x22F3 or PPP code Point 0x005D Ethertype 0x22F3 or PPP code Point 0x005D End of Link Header, not beginning of TRILL Header

TRILL Link Protocols Could you do TRILL over Ethernet over PPP? Of course. Ethernet over PPP is specified. But the extra Ethernet header you have stuck in is useless. It gets thrown away, along with the PPP Header, at the destination TRILL switch port. If the PPP source port has no address, you have to make up fake MAC addresses to put in the useless Ethernet header. July 2014Directory Assist7 TRILL Switch Payload PPP TRILL Switch PPP Link Ethernet

TRILL Link Protocols Similarly, TRILL over a point-to-point pseudowire [RFC 7173] is NOT specified as TRILL over Ethernet over pseudowire. Since there are only two ports on such a link, MAC addresses would be just useless baggage. TRILL over pseudowire is specified as TRILL over PPP over pseudowire because using the PPP codepoints was a convenient way to indicate if the TRILL packet was data or IS-IS. July 2014Directory Assist8

The IP Link Protocol What about TRILL over IP? – (Use of IP does not necessarily imply long distance. You can have a local IP core and long distance carrier Ethernet, for example.) As with any other Link protocol, its purpose is just to get a TRILL packet from one TRILL switch port to another. The source TRILL switch IP port and the destination TRILL switch IP port(s) have IP addresses which are provided by an IP Header. July 2014Directory Assist9

The IP Link Protocol (cont.) The IP Link will be one TRILL hop but may be composed of multiple IP hops. Each IP hop composing the TRILL hop is over some lower layer, possibly different for each hop, and all irrelevant to TRILL. July 2014Directory Assist10 TRILL Switch IP Router Pseudowire IP Hop Ethernet IP Hop TRILL over IP Hop

The IP Link Protocol (cont.) So you have an IP header and a TRILL header. You still need something in between to distinguish data from IS-IS (unless you use up two IP Protocol number and never care about problems with middle boxes due to unknown IP Protocol numbers). July 2014Directory Assist11 IP Header ? TRILL Header

The IP Link Protocol (cont.) You could do TRILL over Ethernet over IP but – You would be adding useless MAC addresses that would be thrown away by the next TRILL switch in the path. If the initial TRILL switch port has no address (e.g., PPP), then you have to make up these useless MAC addresses. – It would be inconsistent with the standardized method of doing TRILL over PPP and TRILL over pseudowire. July 2014Directory Assist12

The IP Link Protocol (cont.) A reasonable choice seems to be UDP. – Destination port values for TRILL Data and IS-IS. – Source port can be used for entropy. – An example of getting two ports and using them to distinguish data from control packets is CAPWAP. July 2014Directory Assist13 IP Header UDP TRILL Header

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